Overhead contact systems, also called catenary systems, have been in use since the 19th century to provide the electrical energy needed to power transit vehicles, such as streetcars, light rail trains and high speed rail trains.
In a typical catenary system, there are two main wires that conduct the electrical power: the messenger wire and the contact wire. The messenger wire serves as the main electrical conductor and supports the contact wire below. The contact wire transfers the electrical power to the motors on the transit vehicle through a current collector, such as a pantograph, typically mounted on the top of the vehicle. The messenger and contact wires are supported by support structures typically placed at 150 foot intervals along the transit system tracks, with the wire run ends approximately 3000 feet in total distance.
Catenary systems have specific requirements for safety and protection of vital system components. These include conformance of the messenger and contact wires to specific geometries to achieve the high speed power collection requirements of transit vehicles.
A key part of catenary systems is maintaining constant tension on the messenger and contact wires as the wires expand and contract as a result of ambient temperature changes. Such tension control is commonly accomplished through use of a constant tensioning system featuring pulleys and a counterweight that moves up and down to counter changes in messenger and contact wire lengths as they stretch (expand) and contract.
A typical prior art constant tensioning system is illustrated in FIGS. 1 and 2. As illustrated in FIG. 1 and described above, a pole 10 supports messenger wire 12 and contact wire 14 at one end, the opposite ends of which are attached in a fixed fashion to a neighboring support pole (as noted above, typically around 3000 feet away). The support pole 10 is hollow and houses a counterweight 16, which is typically a stack of weights, that is suspended and attached to the ends of the messenger wire 12 and contact wire 14 by a counterweight pulley assembly, indicated in general at 18.
As illustrated in FIG. 2, the counterweight pulley assembly 18 uses three pulleys 22a, 22b and 22c, a pulley assembly wire 24 and a yoke plate 26 to control the tension in both the messenger and contact wires. The three pulleys create a three to one ratio on the yoke plate. As a result, however much counterweight there is, three times that, force will be applied to the yoke plate. As illustrated in FIG. 2, the yoke plate has the force applied closer to the messenger wire 12 than the contact wire 14. This offset allows the messenger wire to stay in a higher constant tension with respect to the contact wire. As is known in the art, some constant tensioning systems have different pulley ratios, some have the weights outside the pole, some use H-Beams, I-Beams, etc., but they all typically operate in the same fashion.
In operation, as noted previously, the counterweight 16 of FIG. 1 moves up and down to maintain constant tension in the messenger and contact wires depending on ambient temperature. A cold stop at the upper top limit of counterweight travel is provided by bracket 32, when engaged by counterweight connector 34 (FIG. 1), and a hot stop is provided at the lower bottom limit of counterweight travel by plate 35. As is known in the art, alternative cold and hot stop arrangements may be used.
As with any mechanical device or system, constant tensioning systems can malfunction. Furthermore, obstructions, such as ice or falling tree branches, can occur along the catenary systems between the support poles. This may cause the wires of the catenary system to sag down to an unsafe level.
Furthermore, if the messenger wire and/or the contact wire breaks, live wires could fall to the ground creating a safety hazard. While there are electrical breakers that will typically trip when a ground fault is detected, a live wire could possibly fall without tripping the breaker.
Issues such as those described above are typically determined via visual inspection. Such an approach is time intensive and wasteful of resources. As a result, such inspections may not be performed due to shortage of personal or budget limitations. Such inspections also rely upon the perception and experience level of the individual surveying the catenary and constant tensioning systems. As a result, the accuracy of such an approach may be inconsistent. A better system and approach is needed.